Wildly popular, yet still illegal in the U.S., Internet gaming has earned vast sums for its creators. Meanwhile, a wave of IPOs in Britain has left American banks out of the action

Gambling lore is filled with tales of the lucky novice who walks into a casino and breaks the bank. This year it really happened. The fortunate neophyte is Vikrant Bhargava, who is from Rajasthan, India, and admits that he had never set foot in a casino until recently and still isn't all that fond of gambling. But in a single day in June, he and two colleagues walked away with the poker purse of all time: more than $1 billion in cash.

What distinguishes reality from myth is that Bhargava, 32, wasn't playing poker. He is the marketing director of PartyGaming, a...